Observations by NASA's Mars rover Curiosity have revealed areas with gravel and pebbles that are characteristic of a former riverbed. Researchers, including members of the Niels Bohr Institute, have analysed their shapes and sizes and the rounded pebbles clearly show that there has been flowing water on Mars. The results are published in the scientific journal, Science.

The Mars rover's stereo camera took pictures of a few areas with densely packed pebbles, cemented together like concrete. The image field of an area named Hottah was a mosaic of approximately 1.4 meters x 80 centimeters.